Coupling amplifier



Patented Nov. 26, 1946 UNITED! STATE PAT OFFICE; I I I 2,411,517 I H r I I COUPLING AMPLIFIER HenriG; Busignies, Forest Hills, N; Y., assignor'to' Federal Telephone and Radio Corporation, Newark, N. J'., a corporationof Delaware Application January 16, 1943, Serial,No..4'Z2,589.

' 3 Claims.

This invention relates to improvements in coupling amplifiers, and more particularly to such amplifiers to be used between anginput circuit and a balanced output circuit, as between a directive antenna and its transmission line.

An object of this invention is to provide a novel coupling amplifier between a balanced or a partially unbalanced input circuit and a balanced output circuit.

More specifically, the invention is directed to a novel coupling circuit which amplifies a balanced input, but inherently prevents the amplification and through passage of parallel input currents or voltages to the output circuit.

In another sense, the invention provides a neutralized push-pull amplifier which blocks out unbalanced input currents but amplifies balanced input currents.

These and other objects and advantages of the present invention will appear from the following description of a preferred embodiment thereof, taken in connection with the following drawing in which the single figure is a circuit diagram of a preferred form of coupling amplifier according to the present invention.

In the preferred form of invention illustrated, I use two vacuum tubes I0 and I2 which may be triodes, as illustrated, generally connected in push-pull relationship. Input lead I4 will be connected to the grid of triode III, while input lead I6 will be connected to the grid of triode I2. The output leads I8 and 20 are respectively connected to the anodes of the tubes In and I2 through suitable condensers 22 and 24. In the cathode circuit of each tube is placed a resistor, such as the resistors 26 and 28, the common mid-point between these resistors being grounded. The anodes of the two tubes are serially connected with one another through resistors 30 and 32, the mid-point connection of which is grounded for high frequency currents through the condenser 34. A high voltage source indicated at 35 will also be connected to the mid-point between resistors 30 and 32. Grid-leak resistors 38 and 40 are respectively connected between the individual grids and ground.

In addition to the circuit connectionsjust outlined, it will be also noted that each cathode of the individual tubes is respectively connected to the outputlead of the opposite'tube. For example, the cathode of tube I0 is connected through condenser 42 to the output lead 20, while the cathode of tube I2 is connected through condenser 44 to the output lead] 8. .By means of this cross-connection, a balanced output from the 2 amplifier is assured. For example, if at any chosen instant the polarity of the input lead I4 is positive and the polarity of the input lead I6 is negative, the coupling will act as an amplifier. A negative potential will exist on the output lead I8 due to phase reversal through the tube III while a positive potential will appear on the output lead 20 due to phase reversal through the tube I2. The potential on the output lead I8 derived from the cathode of tube I2 through condenser 44 will likewise be negative, while the potential on the lead 20 derived from the cathode on the tube I 0 through condenser 42 will be positive. Thus, when a balanced load is placed upon the leads I4 and It, a balanced output on the leads I8 and 20 results.

I6, is for example, positive, the amplifier will act to block the passage of current, rather than amplify it. This is due to the fact that while, in such a case, the otential on the lead I8 derived from the anode of the tube III will be negative, the derived voltage values as determined bythe proper adjustment of resistors 28 and 3!] will be of such Value that this potential will be neutralized by the positive potential derived from the cathode of the tube I2. Likewise, by properly proportioning resistors 26 and 32, the negative potential on the lead 29 derived from the anode of the tube I2 will be neutralized by-the potential derived from the cathode of the tube III. The amount of resulting neutralization will, of course, depend upon the amount of unbalance present in the input circuit.

While the invention has beenparticularly described in connection with an amplifier using triodes, it can be adapted for use with other multi-electrode tubes. The described amplifier is particularly well adapted for, use as coupling units between direction finding antennae and transmission lines, in directive antenna'coupling systems and generally in all balanced types of transmission circuits in which the transmission of parallel voltages or currents or straight reception is to be avoided. Furthermore, while, in 7 order to comply with the statutes, I have illustrated and described a single specific embodiment of my invention, it is contemplated that various changes may be made in the circuit as will appear obvious to those skilled in this art and it is therefore to be clearly understood that this descripin the objects and the accompanying claims.

I claim:, I

1. A coupling amplifier comprising a pair of triodes, input leads connected to the grids of said triodes, resistors individually connecting each cathode to ground, a pair of output leads, means for capacitatively coupling one output lead to the anode of one triode and the cathode of the other triode, means for capacitatively coupling the other output lead to the anode of the other triode and the cathode of the one triode, and means including individual resistors and a common condenser for connecting each anode to ground.

2. A coupling amplifier, including in-combination a pair of electron discharge devices each having an anode, a cathode and a grid, a pair of input leads, one connected to each grid, a pair of output leads, a first pair of condensers, one condenser connecting one outlet lead to the anode of one electron discharge device and the other condenser connecting the other output lead to the anode of the other electron discharge device, a second pair of condensers, one condenser connecting the one output lead to the cathode of the other electron discharge device and the other condenser connecting the other output lead to the cathode of the one electron discharge device, a first pair of resistors serially connected between said anodes, a second pair'of resistors serially connected between said cathodes, and means for coupling the mid-points between said pairs of resistors.

3. The combination according to claim 2, in

which said last means is a condenser, in combination with means for grounding the mid-point between said second pair of resistors, and a high potential source connected to the mid-point between said first pair of resistors.

HENRI G. BUSIGNIES. 

